全文获取类型
收费全文 | 234篇 |
免费 | 3篇 |
专业分类
化学 | 120篇 |
晶体学 | 9篇 |
力学 | 8篇 |
数学 | 37篇 |
物理学 | 63篇 |
出版年
2021年 | 2篇 |
2019年 | 5篇 |
2017年 | 2篇 |
2014年 | 10篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 13篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 5篇 |
1970年 | 1篇 |
1929年 | 1篇 |
1923年 | 1篇 |
1893年 | 1篇 |
1891年 | 2篇 |
1889年 | 2篇 |
1874年 | 1篇 |
排序方式: 共有237条查询结果,搜索用时 15 毫秒
11.
Investigations on Metal Catalysts. 37. On the Influence of the Loading on Activity and Selectivity of Supported Nickel Catalysts Strong metal-support interactions effect a distinct decrease of the hydrogenolysis activity. They can be detected with diminishing metal loading in the following order: Ni/TiO2 > Ni/Al2O3 > Ni/SiO2. Strong metal-support interactions mean an influence on the electronic properties of the metal crystallites. On the other hand a mechanical mixture of nickel and η-Al2O3 is more active in hydrogenolysis than nickel. 相似文献
12.
Thermal decomposition of K2SiF6 is a complicated process depending on several parameters, the combination of which cause difficulty in comparing the results obtained from different methods. An experimental method for the study of small quantities of material is described. This allows direct comparison with thermoanalytical results. The influence of experimental conditions is discussed. The decomposition of K2SiF6 is a model for other complexes which produce easily hydrolysed products during thermal reaction. The course of thermal decomposition of K2SiF6 is described up to complete vaporisation of the products at 1200°C. 相似文献
13.
Rippner Blomqvist B Ridout MJ Mackie AR Wärnheim T Claesson PM Wilde P 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):10150-10158
Nonequilibrium interfacial layers formed by competitive adsorption of beta-lactoglobulin and the nonionic triblock copolymer PEO99-PPO65-PEO99 (F127) to the air-water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching), and determinations of foam stability were used as methods. The high surface viscoelasticity, both the shear and dilatational, of the protein films was significantly reduced by coadsorption of polymeric surfactant. The drainage rate of single thin films, in the presence of beta-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than beta-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the nonionic triblock copolymer on the interfacial rheology of beta-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increases the thickness of thin liquid films. In addition, the significant destabilizing effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to long-range steric forces starting to stabilize the foam films at low concentrations of F127. 相似文献
14.
Perfect State Distinguishability and Computational Speedups with Postselected Closed Timelike Curves
Bennett and Schumacher’s postselected quantum teleportation is a model of closed timelike curves (CTCs) that leads to results
physically different from Deutsch’s model. We show that even a single qubit passing through a postselected CTC (P-CTC) is
sufficient to do any postselected quantum measurement with certainty, and we discuss an important difference between “Deutschian”
CTCs (D-CTCs) and P-CTCs in which the future existence of a P-CTC might affect the present outcome of an experiment. Then,
based on a suggestion of Bennett and Smith, we explicitly show how a party assisted by P-CTCs can distinguish a set of linearly
independent quantum states, and we prove that it is not possible for such a party to distinguish a set of linearly dependent
states. The power of P-CTCs is thus weaker than that of D-CTCs because the Holevo bound still applies to circuits using them,
regardless of their ability to conspire in violating the uncertainty principle. We then discuss how different notions of a
quantum mixture that are indistinguishable in linear quantum mechanics lead to dramatically differing conclusions in a nonlinear
quantum mechanics involving P-CTCs. Finally, we give explicit circuit constructions that can efficiently factor integers,
efficiently solve any decision problem in the intersection of NP and coNP, and probabilistically solve any decision problem
in NP. These circuits accomplish these tasks with just one qubit traveling back in time, and they exploit the ability of postselected
closed timelike curves to create grandfather paradoxes for invalid answers. 相似文献
15.
A measure called physical complexity is established and calculated for a population of sequences, based on statistical physics, automata theory, and information theory. It is a measure of the quantity of information in an organism’s genome. It is based on Shannon’s entropy, measuring the information in a population evolved in its environment, by using entropy to estimate the randomness in the genome. It is calculated from the difference between the maximal entropy of the population and the actual entropy of the population when in its environment, estimated by counting the number of fixed loci in the sequences of a population. Up until now, physical complexity has only been formulated for populations of sequences with the same length. Here, we investigate an extension to support variable length populations. We then build upon this to construct a measure for the efficiency of information storage, which we later use in understanding clustering within populations. Finally, we investigate our extended physical complexity through simulations, showing it to be consistent with the original. 相似文献
16.
Weijie Chen Dr. YoungKu Kang Dr. Richard G. Wilde Prof. Dr. Daniel Seidel 《Angewandte Chemie (International ed. in English)》2014,53(20):5179-5182
In contrast to the continuously growing number of methods that allow for the efficient α‐functionalization of amines, few strategies exist that enable the direct functionalization of amines in the β‐position. A general redox‐neutral strategy is outlined for amine β‐functionalization and α,β‐difunctionalization that utilizes enamines generated in situ. This concept is demonstrated in the context of preparing polycyclic N,O‐acetals from simple 1‐(aminomethyl)‐β‐naphthols and 2‐(aminomethyl)‐phenols. 相似文献
17.
Hydrogen atoms adsorbed on Si(111) and Pt(111) were investigated by nuclear reaction analysis (NRA) using 1H(15N,alphagamma)12C. From measurements of the NRA spectrum at normal and tilted ion incidences the zero-point vibrational energies of H on Si(111) in the perpendicular and parallel directions were found to be 123.4+/-4.6 and 44.6+/-6.2 meV, respectively, which are consistent with harmonic potentials. The zero-point energies obtained for Pt(111)-H were 80.8+/-3.9 and 62.1+/-6.0 meV for perpendicular and parallel directions, respectively. These results indicate that the stretching mode is harmonic, while the bending mode is strongly anharmonic. 相似文献
18.
Investigations on Metal Catalysts. XXVII. On the Influence of Several Carriers on the Dispersion of Nickel Nickel supported catalysts (carrier: η-, ?-, α-Al2O3, TiO2) were characterized by chemically determined degree of reduction, CO chemisorption, magnetic susceptibility measurements and FMR. The influence of interaction between carrier and active component in the unreduced state on the size and number of Ni crystallites is discussed. 相似文献
19.
Ohne Zusammenfassung 相似文献
20.
Solvent activities and molal osmotic coefficients have been determined in the ternary system water—calcium chloride—urea at 298.15 K by means of an isopiestic method. Thermodynamic expressions are used to calculate molal activity coefficients of the solutes as well as Gibbs free energies of transfer from binary to ternary solutions.In the title system, the strong interactions of the dissolved components are indicated by the high, negative GE values and the non-linear course of the isolines of solvent activity. 相似文献